基于交流小信号注入的不准确馈线阻抗孤岛微网频率恢复控制策略

With the “Dual-carbon” strategy proposed in China, the microgrid composed of distributed generations has become an effective way to solve the energy crisis and environmental pollution problems. To improve the power quality of a microgrid system, frequency restoration control is usually added to distributed generations to compensate for the frequency deviation caused by changes in load. It is necessary to obtain the information about accurate feeder impedance when calculating the load terminal frequency, so as to reduce the reliance of the system on high-speed communication. However, this is often difficult to be guaranteed in practical engineering, thus leading to the difference of power distribution among distributed generations and eventually deteriorating the frequency stability of the system. To solve these problems, the mechanism of an unstable system caused by the inaccurate feeder impedance is analyzed, and it is pointed out that the calculation error of load terminal frequency is the basic cause of power distribution difference among distributed generations. On this basis, a frequency restoration control strategy based on small-AC-signal injection is proposed. By adding an additional small-AC-signal to the output voltage from each distributed generation, a droop relationship between the injected small-AC-signal frequency and the calculated value of load terminal frequency is established, and the active power of the small signal is used to compensate for the calculated deviation of load terminal frequency caused by the inaccurate feeder impedance, so as to realize the compensation for frequency deviation while maintaining the power sharing of the system. To illustrate the application scope of this control strategy, the differential-mode small-signal model of a typical microgrid system is established, and the design method for related parameters is discussed. Finally, the effectiveness of the proposed method was verified by a hardware-in-the-loop experiment.